Israel has admitted obtaining several U.S.-made timing devices that can be used to manufacture atomic weapons but denied that any of the devices were used for nuclear purposes or sent to other countries.

The admission was made by the Israeli Defense Ministry Sunday after Newsweek magazine reported that a federal grand jury in Los Angeles is investigating whether the devices, known as krytrons, were smuggled from the United States in violation of U.S. export laws.

If Israel is found to have been involved in smuggling the devices, the situation could have major international consequences, including possible cutoff of all U.S. aid to Israel, which is the largest recipient of American foreign assistance.

Legislation recently introduced by Rep. Stephen J. Solarz (D-N.Y.) would bar aid to any country violating U.S. export laws for production of nuclear explosive devices.

Israeli Embassy sources here said they understand that the matter is being probed by a Los Angeles grand jury.

But the sources, who declined to be identified, said they are confident that investigation will show the Israeli government was not involved in wrongdoing or other activities that could affect U.S. aid.

A spokesman for the U.S. attorney's office in Los Angeles refused comment on whether a grand jury investigation is under way.

State Department spokesman Ed Djerejian said in response to questions about the Newsweek report: "As a general policy, we do not comment on any matter that is under investigation by the law-enforcement authorities. I can say, however, that we have consistently stressed to law-enforcement authorities the importance we attach to the vigorous enforcement of U.S. export-control laws."

Israel's statement, reported prominently in the Israeli press yesterday, was silent on the issue of whether U.S. laws had been broken.

It said only that the Israeli government, acting on an official U.S. request for information, had determined that, between 1979 and 1983, an unspecified number of krytrons had been shipped to an Israeli firm under contract to the government for defense work.

The statement added that the devices were used only in conventional research and development and testing equipment, that none had been sent to other countries and that a recent check showed that all of the krytrons are still in Israel.

The statement did not identify the firm involved. Newsweek quoted Israeli sources as saying Arnon Milchan, an Israeli businessman and film producer, was implicated.

The magazine added that Milchan, contacted in Paris, denied knowledge of the affair and said he had not been active in the affairs of his Tel Aviv firm, Milchan Bros. Ltd., for 12 years.